• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 16 subscribers
  • Views 262 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TRF7960A: Permanent carrier signal on TX_OUT pin even if tranciever is off

Igor Fadeev1
Prodigy 30 points
Part Number: TRF7960A

Hello!

I have a board with STM32F777 MCU and TRF7960A chip connected via SPI with 1.875 MHz frequency.
Chip is initialized using sloa227b library according to the specific of the trf7960A chip. I can read and write data to registers, for example I changed Bits 4 & 5 of the 0x09 register and saw with the oscilloscope the frequencies 13.6, 6.8, 3.4 & 0 MHz on the SYS_CLK pin.

But on TX_OUT pin the carrier signal is presented even if bit 5 in 0x00 register is set to zero, which means that transmitter is off. What can be the problem?

Best regards

  • 0
    TI__Guru*** 131470 points

    Hello Igor,

    Did you account for the SPI polarity swaps on both reads and writes for all registers? SLOA227 didn't include any support for TRF7960A SPI issues.

    The TRF7960A has a number of quirks with SPI that you should make sure are handled right, can you check your firmware and SPI settings against these guidelines: https://www.ti.com/lit/pdf/sloa155

    Also the minimum SPI clock is supposed to be 2MHz. You are very close to that, but I would say try a bit faster to also rule out that the SPI clock frequency is outside of the datasheet specifications.

  • 0 in reply to Ralph Jacobi
    Prodigy 30 points

    Thank for the response, Ralph!

    Yes, I made a SPI polarity swap using sloa140b doc, that's why I can read and write register 0x09 and change SYS_CLK frequency. 

    I increased SPI clock in 2 times. Chip Status Control Register (0x00) has value 0x01 but on TX_OUT pin I still see the 13.6 MHz signal

  • 0 in reply to Igor Fadeev1
    TI__Guru*** 131470 points

    Hello Igor,

    On how many boards do you see this behavior? And is it outputting at full voltage or at a reduced voltage?

    Is this on a custom board or a TI EVM?

    What happens if you set the TX to be in half-power mode?

    What is your regulator control setting (Register 0x0B) and VIN to the device?

  • 0 in reply to Ralph Jacobi
    Prodigy 30 points

    Hello Ralph,

    I have 1 custom board with trf7960A chip. Setting half-power to the 0x00 chip status register gives ~3V output signal. Setting Full-power gives 5V output signal on TX_OUT pin. 
    Vin = 5V, Regulator Control Register 0x0B is set to default state (0x87), I didn't change it.

  • 0 in reply to Igor Fadeev1
    TI__Guru*** 131470 points

    Hello Igor,

    If it is just one board, I am wondering if there is potential of damage to the device then. Can you swap the IC with a new one and see if the behavior still occurs? I have not heard of this issue before so to hear only one board is impacted makes me think perhaps the device got ESD damaged.